1. Field of Invention
The present invention relates to an installation capable of increasing the usable range of a light source. More particularly, the present invention relates to an installation capable of increasing the usable range along the axial direction of a light source.
2. Description of Related Art
The operating principles of most image-extraction instruments, such as scanners and digital cameras, are very similar. Common features of image-extraction instruments include the use of a light source to produce an optical image and the passing of an optical image through an optical transmission system to an optical sensor. In general, the optical sensor is a charge couple device (CCD).
However, the longitudinal light source of a scanner has one major drawback, namely, brightness level along the central portion of the light axis is usually higher than along the adjacent sides. Hence, an image produced by the light source is brighter in the middle while dimmer along the edges. Since a scanner depends on brightness contrast to operate, a conventional scanner has poorer contrast near the two edges of the light axis. To preserve quality of the scan image, a section near the edge regions is often unused.
Hence, reducing brightness level variation along the axial direction of a light source has become one of the major improvement targets. For example, in Taiwan patent publication no. 244013 entitled xe2x80x98Improved lamp shade compensation of an optical scannerxe2x80x99, brightness variation along the light axis is improved by modifying the lamp shade structure. However, the invention requires specially made components, and hence may lead to an increase in production cost.
In Taiwan patent publication no. 352886 entitled xe2x80x98A lens structure and its integration with an image-reading devicexe2x80x99, another method of improving brightness level along the axial direction of a light source is proposed. By changing the degree of reflectivity of a coated film on the reflecting lens inside the scanner, brightness level variation is reduced. However, the reflectivity of more than one reflecting lens needs to be modified, thereby increasing the production cost necessary for achieving the results. In addition, the method is not suitable for other optical sensing devices besides a scanner.
Accordingly, one object of the present invention is to provide an installation for increasing the scanning range along the axial direction of a light source by changing the light transparency of the transparent panel leading to an optical sensor. In addition, the installation can be applied to other optical devices besides a scanner,such as a digital. camera.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an installation for increasing the scanning range of a light source. The installation includes a light source and an optical sensor. The light source is used as a source for generating the image to be detected. The optical sensor includes a sensor and a transparent panel. The transparent panel is positioned between the sensor and the light source. Furthermore, the transparent panel also has a long axis that runs from edge to edge passing through the panel. The sensor receives an optical image formed by projecting light from the light source through the transparent panel. There is a coating over the transparent panel such that light transparency in the middle section of the long axis is higher than either side.
The coating can be deposited over the entire transparent panel. The coating can be deposited over the imaging section on the transparent panel only. In addition, the coating can be made by forming a plurality of coating materials of the same thickness over surface regions of the transparent panel so that a range of light transparencies are obtained across the panel. Conversely, a coating made from a single material but having a variable thickness is formed across the transparent panel to obtain a range of light transparencies across the panel.
In this invention, a coating is added onto the transparent panel of an optical sensor so that light transparency varies across the panel. Hence, there is no need to produce or modify components. Therefore, this invention is able to improve brightness variation of a light source with only minimum modification of the components. In addition, the installation can be applied to other optical devices besides a scanner, such as a digital camera.